Devices and methods herein generally relate to machines such as printers and/or copier devices and, more particularly, to gripper architecture for sheet conveyance.
Marking systems that transport paper or other media are well known in the art. These marking systems include electrostatic marking systems, non-electrostatic marking systems, printers, or any other marking system where paper, or other flexible media or sheets, are transported internally.
In printing systems, there exist a variety of systems and methods for handling sheets of different sizes. Some systems convey sheets via systems of belts or rollers, which provide superb flexibility for sheets of different sizes. But, in these systems, slippage between sheets and their conveyance mechanism can create mis-registration between sheets and the printed image that is applied to them.
The gripper-based architecture of traditional offset lithography provides the most robust system for sheet registration. This is because, in a gripper-based architecture, once a sheet is seized in a gripper, it remains rigidly clamped in that gripper (or is passed via a system with high mechanical tolerances to subsequent grippers) until all printing processes are completed.
However, because lithographic systems are based on a master (printing plate) of typically fixed size, lithographic gripper-system architectures are ill suited for adaptation to digital printing systems where sheet size might be variable. While one might propose creation of a system with multiple grippers positioned for multiple sheet lengths, in practice such a system would induce print quality defects for long sheets, the cause of the defects being the unsupported portion of the sheet that bridges the gap where the additional short-sheet grippers are located. Due to the unwanted gap, heretofore, a multiple-gripper-for-multiple sheet-length architecture was not practical. Hence, the cadence of gripping relative to sheet velocity is fixed at a single value.
A principle advantage of digital printing is that small sheets may be printed at a faster rate (commensurate with their length) than larger sheets. But digital architectures have heretofore been unable to enjoy the image-to-paper registration precision characteristics of a gripper system, while maintaining the advantage of efficient rates on smaller sheets. Architectures could achieve registration precision or speed efficiency across sizes, but not both.